Ultrasonic tee probe with two dimensional array transducer

ABSTRACT

A semi-invasive ultrasound imaging system for imaging biological tissue includes a transesophageal probe or a transnasal, transesophageal probe connected to a two-dimensional ultrasound transducer array, a transmit beamformer, a receive beamformer, and an image generator. The two-dimensional transducer array is disposed on a distal portion of the probe&#39;s elongated body. The transmit beamformer is connected to the transducer array and is constructed to transmit several ultrasound beams over a selected pattern defined by azimuthal and elevation orientations. The receive beamformer is connected to the transducer array and is constructed to acquire ultrasound data from the echoes reflected over a selected tissue volume. The tissue volume is defined by the azimuthal and elevation orientations and a selected scan range. The receive beamformer is constructed to synthesize image data from the acquired ultrasound data. The image generator is constructed to receive the image data and generate images that are displayed on an image display. Preferably, the image generator is constructed to generate, from the image data, several orthographic projection views over the selected tissue volume.

This is a divisional application of U.S. Ser. No. 09/919,464, filed Jul.31, 2001, now U.S. Pat. No. 6,572,547 and entitled “TRANSESOPHAGEAL ANDTRANSNASAL, TRANSESOPHAGEAL ULTRASOUND IMAGING SYSTEMS.”

The present invention relates to semi-invasive ultrasound imagingsystems, and more particularly to transesophageal imaging systems andtransnasal, transesophageal imaging systems that provide severaltwo-dimensional plane views and projection views for visualizingthree-dimensional anatomical structures inside a patient.

Non-invasive, semi-invasive and invasive ultrasound imaging has beenwidely used to view tissue structures within a human body, such as theheart structures, the abdominal organs, the fetus, and the vascularsystem. The semi-invasive systems include transesophageal imagingsystems, and the invasive systems include intravascular imaging systems.Depending on the type and location of the tissue, different systemsprovide better access to or improved field of view of internalbiological tissue.

In general, ultrasound imaging systems include a transducer arrayconnected to multiple channel transmit and receive beamformers. Thetransmit beamformer applies electrical pulses to the individualtransducers in a predetermined timing sequence to generate transmitbeams that propagate in predetermined directions from the array. As thetransmit beams pass through the body, portions of the acoustic energyare reflected back to the transducer array from tissue structures havingdifferent acoustic characteristics. The receive transducers (which maybe the transmit transducers operating in a receive mode) convert thereflected pressure pulses into corresponding electrical RF signals thatare provided to the receive beamformer. Due to different distances froma reflecting point to the individual transducers, the reflected soundwaves arrive at the individual transducers at different times, and thusthe RF signals have different phases.

The receive beamformer has a plurality of processing channels withcompensating delay elements connected to a summer. The receivebeamformer selects the delay value for each channel to combine echoesreflected from a selected focal point. Consequently, when delayedsignals are summed, a strong signal is produced from signalscorresponding to this point. However, signals arriving from differentpoints, corresponding to different times, have random phaserelationships and thus destructively interfere. The receive beamformerselects such relative delays that control the orientation of the receivebeam with respect to the transducer array. Thus, the receive beamformercan dynamically steer the receive beams to have desired orientations andcan focus them at desired depths. The ultrasound system thereby acquiresacoustic data.

To view tissue structures in real-time, various ultrasound systems havebeen used to generate two-dimensional or three-dimensional images. Atypical ultrasound imaging system acquires a two-dimensional image planethat is perpendicular to the face of the transducer array applied to apatient's body. To create a three-dimensional image, the ultrasoundsystem must acquire acoustic data over a three-dimensional volume by,for example, moving a one-dimensional (or a one-and-half dimensional)transducer array over several locations. Alternatively, atwo-dimensional transducer array can acquire scan data over amultiplicity of image planes. In each case, the system stores the imageplane data for reconstruction of three-dimensional images. However, toimage a moving organ, such as the heart, it is important to acquire thedata quickly and to generate the images as fast as possible. Thisrequires a high frame rate (i.e., the number of images generated perunit time) and fast processing of the image data. However, spatialscanning (for example, when moving a one-dimensional array over severallocations) is not instantaneous. Thus, the time dimension is intertwinedwith the three space dimensions when imaging a moving organ.

Several ultrasound systems have been used to generate 3D images by dataacquisition, volume reconstruction, and image visualization. A typicalultrasound system acquires data by scanning a patient's target anatomywith a transducer probe and by receiving multiple frames of data. Thesystem derives position and orientation indicators for each framerelative to a prior frame, a reference frame or a reference position.Then, the system uses the frame data and corresponding indicators foreach frame as inputs for the volume reconstruction and imagevisualization processes. The 3D ultrasound system performs volumereconstruction by defining a reference coordinate system within whicheach image frame in a sequence of the registered image frames. Thereference coordinate system is the coordinate system for a 3D volumeencompassing all image planes to be used in generating a 3D image. Thefirst image frame is used to define the reference coordinate system (andthus the 3D volume), which has three spherical axes (r_(v), θ_(v) andφ_(v) axes) three orthogonal axes (i.e., x_(v), y_(v) and z_(v) axes).Each image frame is a 2D slice (i.e., a planar image) has two polar axes(i.e., r_(i) and φ_(i) axes) or two orthogonal axes (i.e., x_(i) andy_(i)), where i is the i-th image frame. Thus, each sample point withinan image plane has image plane coordinates in the image plane coordinatesystem for such image plane. To register the samples in the referencecoordinate system, the sample point coordinates in the appropriate imageplane coordinate system are transposed to the reference coordinatesystem. If an image plane sample does not occur at specific integercoordinates of the reference coordinate system, the system performsinterpolation to distribute the image plane sample among the nearestreference coordinate system points.

To store sample data or the interpolated values derived from the sampledata, the system allocates memory address space, wherein the memory canbe mapped to the reference coordinate system. Thus, values for a givenrow of a given reference volume slice (taken along, for example, thez-axis) can be stored in sequential address locations. Also, values foradjacent rows in such slice can be stored in adjacent first memoryaddress space. The system can perform incremental reconstruction bycomputing a transformation matrix that embodies six offsets. There arethree offsets for computing the x, y, and z coordinates in thex-direction (along the row of the image), and three offsets forcomputing the x, y, and z coordinates in the y-direction (down thecolumn of the image). Then, the system computes the corners of thereconstruction volume and compares them with the coordinates of thebounding volume. Next, the system determines the intersecting portion ofthe acquired image and the bounding coordinates and converts them backto the image's coordinate system. This may be done using several digitalsignal processors.

Furthermore, the system can compute an orthogonal projection of thecurrent state of the reconstruction volume. An orthogonal projectionuses simpler computation for rendering (no interpolations need to becomputed to transform from the reference coordinate system to adisplayed image raster coordinate system). The system can use a maximumintensity projection (MIP) rendering scheme in which a ray is cast alongthe depth of the volume, and the maximum value encountered is the valuethat is projected for that ray (e.g., the value used to derive a pixelfor a given raster point on the 2D image projection). The systemincrementally reconstructs and displays a target volume in real time.The operator can view the target volume and scan effectiveness in realtime and improve the displayed images by deliberately scanning desiredareas repeatedly. The operator also can recommence volume reconstructionat the new viewing angle.

The image visualization process derives 2D image projections of the 3Dvolume over time to generate a rotating image or an image at a newviewing angle. The system uses a shear warp factorization process toderive the new 2D projection for a given one or more video frames of theimage. For each change in viewing angle, the process factorizes thenecessary viewing transformation matrix into a 3D shear which isparallel to slices of the volume data. A projection of the shear forms a2D intermediate image. A 2D warp can be implemented to produce the finalimage, (i.e., a 2D projection of the 3D volume at a desired viewingangle). The system uses a sequence of final images at differing viewingangles to create a real-time rotating view of the target volume.

Other systems have been known to utilize power Doppler images alone in athree dimensional display to eliminate the substantial clutter caused bystructural information signals. Such Doppler system stores Doppler powerdisplay values, with their spatial coordinates, in a sequence of planarimages in an image sequence memory. A user can provide processingparameters that include the range of viewing angles. For instance, theuser can input a range of viewing angles referenced to a line of view ina plane that is normal to the plane of the first image in the sequence,and a range increment. From these inputs the required number of threedimensional projections is computed. Then, this system forms thenecessary sequence of maximum intensity projections by first recallingthe planar Doppler power images from the image sequence memory forsequential processing by a scan converter and display processor. Theprocessor rotates each planar image to one of the viewing anglesprojected back to the viewing plane.

The Doppler system accumulates the pixels of the projected planar imageson a maximum intensity basis. Each projected planar image is overlaidover the previously accumulated projected images but in a transposedlocation in the image plane which is a function of the viewing angle andthe interplane spacing: the greater the viewing angle, the greater thetransposition displacement from one image to the next. The displaypixels chosen from the accumulated images are the maximum intensitypixels taken at each point in the image planes from all of the overlaidpixels accumulated at each point in the image. This effectively presentsthe maximum intensity of Doppler power seen by the viewer along everyviewing line between the viewer and the three dimensionalrepresentation.

This system can rotate, project, transpose, overlay, and choose themaximum intensities at each pixel for all of the planar images, and thenstore in the image sequence memory the resulting three dimensionalrepresentation for the viewing angle. The stored three dimensionalsequence is available for recall and display upon command of the user.As the sequence is recalled and displayed in real time, the user can seea three dimensional presentation of the motion or fluid flow occurringin the volumetric region over which the planar images were acquired. Thevolumetric region is viewed three dimensionally as if the user weremoving around the region and viewing the motion or flow from changingviewing angles. The viewer can sweep back and forth through thesequence, giving the impression of moving around the volumetric regionin two directions.

It has also been known to utilize a modified two dimensional ultrasonicimaging system to provide three dimensional ultrasonic images. Suchthree dimensional ultrasonic imaging system can use conventional twodimensional ultrasonic imaging hardware and a scan converter. The twodimensional ultrasonic imaging system acquires a plurality of twodimensional images. This system processes the images through scanconversion to approximate their rotation to various image planes andprojection back to a reference plane, which can be the original imageplane. Conventional scan conversion hardware can be used to rescale thesector angle or depth of sector images, or the aspect ratio ofrectangular images. This system projects a plurality of planes for eachimage and then stores them in a sequence of combined images, whereineach combined image comprises a set of corresponding projected imagesoffset with respect to each other. Each combined image is a differentview of a three dimensional region occupied by the planar imageinformation.

The above system can replay the sequence of combined images on a displayto depict the three dimensional region as if it is rotating in front ofa viewer. Furthermore, the system can recall the stored combined imageson the basis of the three dimensional viewing perspectives and displayedsequentially in a three dimensional presentation.

There are several medical procedures where ultrasound imaging systemsare not yet widely used. Currently, for example, interventionalcardiologists use mainly fluoroscopic imaging for guidance and placementof devices in the vasculature or in the heart. These procedures areusually performed in a cardiac catheterization laboratory (Cathlab) oran electrophysiology laboratory (Eplab). During cardiac catheterization,a fluoroscope uses X-rays on a real-time frame rate to give thephysician a transmission view of a chest region, where the heartresides. A bi-plane fluoroscope, which has two transmitter-receiverpairs mounted at 90° to each other, provides real-time transmissionimages of the cardiac anatomy. These images assist the physician inpositioning various catheters by providing him (or her) with a sense ofthe three-dimensional geometry of the heart.

While fluoroscopy is a useful technique, it does not provide highquality images with good contrast in soft tissues. Furthermore, thephysician and the assisting medical staff need to cover themselves witha lead suit and need to reduce the fluoroscopic imaging time wheneverpossible to lower their exposure to X-rays. In addition, fluoroscopy maynot be available for some patients, for example, pregnant women, due tothe harmful effects of the X-rays. Recently, transthoracic andtransesophageal ultrasound imaging have been very useful in the clinicaland surgical environments, but have not been widely used in the Cathlabor Eplab for patients undergoing interventional techniques.

Therefore there is a need for transesophageal or transnasal,transesophageal ultrasound systems and methods that can provide fast andcomputationally inexpensive real-time imaging. The images should enableeffective visualization of the internal anatomy that includes variousstructures and provide selected views of the tissue of interest. Anultrasound system and method providing anatomically correct and easilyunderstandable, real-time images would find additional applications inmedicine.

The present invention relates to novel transesophageal ultrasoundapparatuses or methods for imaging three-dimensional anatomicalstructures and/or medical devices (e.g., therapy devices, diagnosticdevices, corrective devices, stents) introduced inside a patient.

According to one aspect, a transesophageal ultrasound imaging system forimaging biological tissue includes a transesophageal probe connected toa two-dimensional ultrasound transducer array, a transmit beamformer, areceive beamformer, and an image generator. The two-dimensionaltransducer array is disposed on a distal portion of the probe'selongated body. The transmit beamformer is connected to the transducerarray and is constructed to transmit several ultrasound beams over aselected pattern defined by azimuthal and elevation orientations. Thereceive beamformer is connected to the transducer array and isconstructed to acquire ultrasound data from the echoes reflected over aselected tissue volume. The tissue volume is defined by the azimuthaland elevation orientations and a selected scan range. The receivebeamformer is constructed to synthesize image data from the acquiredultrasound data. The image generator is constructed to receive the imagedata and generate images of the selected tissue volume that aredisplayed on an image display (a video display, a printer, etc.).

Preferred embodiments of this aspect include one or more of thefollowing features:

The image generator is constructed to generate, from the image data, atleast two orthographic projection views over the selected tissue volume,and the image display is constructed to display the at least twoprojection views.

The ultrasound imaging system may include a surface detector and acontrol processor. The surface detector is constructed to receive imageparameters from the control processor and generate surface data from theimage data. The image generator is constructed to generate from thesurface data a projection image for display on the image display.

The surface detector is a B-scan boundary detector and the imagegenerator is constructed to generate from the image data and the surfacedata a plane view including the projection image. Furthermore, the imagegenerator may be constructed to generate, from the image data and thesurface data, at least two orthographic projection views each includingthe plane view and the projection image. The surface detector may be aC-scan boundary detector and the image generator is then constructed togenerate a C-scan view.

The ultrasound imaging system includes a probe that is a transesophagealprobe or a transnasal transesophageal probe. The transesophageal probeincludes a locking mechanism co-operatively arranged with anarticulation region of the probe and constructed to lock in place thetransducer array after orienting the array relative to a tissue regionof interest. The transnasal transesophageal probe includes a lockingmechanism co-operatively arranged with an articulation region of theprobe and constructed to lock in place the transducer array afterorienting the array relative to a tissue region of interest.

The transducer array and the beamformers are constructed to operate in aphased array mode and acquire the ultrasound data over the selectedazimuthal range for several image sectors each having a designatedelevation location. The transducer array includes a plurality ofsub-arrays connected to the transmit and receive beamformers.

The image generator is constructed to generate, from the image data, atleast two orthographic projection views over the selected tissue volume,and the image display is constructed to display the at least twoprojection views. The image generator is constructed to generate two ofthe orthographic projection views as orthogonal B-scan views andgenerate one of the orthographic projection views as a C-scan view.

The transesophageal probe may also include a locking mechanismco-operatively arranged with an articulation region of the probe andconstructed to lock in place the transducer array after orienting thearray relative to a tissue region of interest.

The ultrasound imaging system includes a control processor constructedand arranged to control the transmission of the ultrasound beams andcontrol the synthesis of the image data based on range data provided bya user. The transducer array includes a plurality of sub-arraysconnectable to the transmit and receive beamformers and the controlprocessor is constructed to control arrangement of the sub-arrays foroptimizing acquisition of the echo data of the tissue volume. Thecontrol processor constructed and arranged to provide to the transmitbeamformer and the receive beamformer scan parameters that include animaging depth, a frame rate, or an azimuth to elevation scan ratio.

The control processor is constructed to receive input data and provideoutput data causing the transmit and receive beamformers to change theazimuthal range. The control processor is constructed to receive inputdata and provide output data causing the transmit and receivebeamformers to change the elevation range. The control processor isconstructed to provide data to image generator for adjusting a yaw ofthe views by recalculating the orthographic projection views. Bychanging the azimuthal range or the elevation range, a clinician candirect the scan over a smaller data volume centered on the tissue ofinterest. By scanning over the smaller volume, the system improvesreal-time imaging of moving tissue by increasing the frame rate, becauseit collects a smaller number of data points.

The image generator includes at least one view interpolation processorconstructed to generate the at least two orthographic projection views,at least one icon generator constructed to generate the at least twoicons associated with the at least two orthographic projection views,and includes at least one boundary detector constructed and arranged todetect a tissue boundary.

The view interpolation processor is arranged to generate a B-scan viewand a C-scan view, the C-scan view is generated by receiving C-scandesignation information from the B-scan view. The view interpolationprocessor is an azimuthal view interpolation processor. The viewinterpolation processor is an elevation view interpolation processor.The view interpolation processor includes a gated peak detector.

The boundary detector is a B-scan boundary detector and theinterpolation processor is further arranged to receive from the B-scanboundary detector data for highlighting borders in the orthographicprojection views. The boundary detector is a C-scan boundary detectorand the interpolation processor is further arranged to receive from theC-scan boundary detector data for highlighting borders in theorthographic projection views.

The image generator includes a yaw adjustment processor. The imagegenerator includes a range processor constructed to provide two rangecursors for generating a C-scan projection view. The range processor isarranged to receive a user input defining the two range cursors. Theicon generator constructed to generate an azimuthal icon displaying theazimuthal angular range and displaying a maximum azimuthal angularrange. The icon generator constructed to generate an elevation icondisplaying the elevation angular range and displaying a maximumelevation angular range.

According to another aspect, a transesophageal ultrasound imaging methodis performed by introducing into the esophagus a transesophageal probeand positioning a two-dimensional ultrasound transducer array at aselected orientation relative to an tissue region of interest,transmitting ultrasound beams over a plurality of transmit scan linesfrom the transducer array over a selected azimuthal range and a selectedelevation range of locations, and acquiring by the transducer arrayultrasound data from echoes reflected from a selected tissue volumedelineated by the azimuthal range, the elevation range and a selectedsector scan depth and synthesizing image data from the acquiredultrasound data. Next, the ultrasound imaging method is performed bygenerating images from the image data of the selected tissue volume, anddisplaying the generated images.

Preferably, the transesophageal ultrasound imaging method may beperformed by one or more of the following: The transmitting and theacquiring is performed by transmit and receive beamformers constructedto operate in a phased array mode and acquire the ultrasound data overthe selected azimuthal range for several image sectors having knownelevation locations. The generating includes generating at least twoorthographic projection views over the tissue volume, and the displayingincludes displaying at least two orthographic projection views.

The imaging method may be used for positioning a surgical instrument ata tissue of interest displayed by the orthographic projection views. Theimaging method may be used for verifying a location of the surgicalinstrument during surgery based orthographic projection views. Theimaging method may be used for performing the transmitting, theacquiring, the generating, and the displaying of the orthographicprojection views while performing surgery with the surgical instrument.The imaging method may be used for performing the transmitting, theacquiring, the generating, and the displaying of the orthographicprojection views after performing surgery with the surgical instrument.

The generation of at least two orthographic projection views may includegenerating a selected C-scan view. The generation of the selected C-scanview may include providing a C-scan designation for the selected C-scanview. The designation may include defining a bottom view or defining atop view. The generation of the C-scan may include detecting a tissueboundary by using a C-scan boundary detector, and selecting ultrasounddata for the C-scan by a gated peak detector.

The imaging method may include providing input data to a controlprocessor and providing output data from the control processor to directthe transmit and receive beamformers to change the azimuthal range. Theimaging method may include providing input data to a control processorand providing output data from the control processor to direct thetransmit and receive beamformers to change the elevation range. Thecontrol processor may also provide data to image generator for adjustinga yaw of the views by recalculating the orthographic projection views.By changing the azimuthal range or the elevation range, a clinician candirect the scan over a smaller data volume centered on the tissue ofinterest. By scanning over the smaller volume, the system improvesreal-time imaging of moving tissue by increasing the frame rate, becauseit collects a smaller number of data points.

The generation of at least two orthographic projection views may includegenerating an azimuthal icon associated with the selected azimuthalrange and a maximum azimuthal range, or an elevation icon associatedwith the selected elevation range and a maximum elevation range.

Brief description of the drawings:

FIG. 1 illustrates an ultrasound system including a transesophagealimaging probe having a distal part and a semi-flexible elongated body.

FIGS. 2 and 2A are schematic cross-sectional views of a rigid region ofthe transesophageal imaging probe.

FIG. 3 shows a schematic cross-sectional view of an articulation regionof the transesophageal probe articulated as an in-plane J hook.

FIG. 3A shows a schematic cross-sectional view of the articulationregion of the transesophageal probe articulated as an out-of-plane Jhook.

FIG. 3B shows a schematic cross-sectional view of the articulationregion of the transesophageal probe articulated as an in-plane S hook.

FIG. 3C is a perspective view of an articulation link used in thearticulation region of the transesophageal probe.

FIG. 4 shows a scanned volume of echo data used for illustration oforthographic projection views.

FIGS. 4A, 4B, 4C, 4D and 4E show different orientations of the scannedvolumes generated by articulating the distal part as described inconnection with FIGS. 3 through 3B.

FIGS. 5(1)-5(5) show diagrammatically an image generator of theultrasound system of FIG. 1.

FIGS. 5A(1)-5A(2) show diagrammatically a control processor of theultrasound system of FIG. 1.

FIG. 5B shows diagrammatically an array of ultrasound transducersconnected to a transmit beamformer and a receive beamformer of theultrasound system.

FIG. 5C shows diagrammatically a gated peak detector used in the shownin FIG. 5.

FIGS. 5(1)-5(5), 5(A) (1)-5(A) (2) show diagrammatically the imagingsystem according to a presently preferred embodiment. The entireoperation of the imaging system is controlled by a control processor140, shown in FIGS. 5A(1)-5A(2). Control processor 140 receives inputcommands from input controls 142 through 167 and provides output controlsignals 170 through 191. Control processor 140 provides control data toa beamformer 200, and provides image control data to image generator250, which includes processing and display electronics. Beamformer 200includes transmit beamformer 200A and a receive beamformer 200B, showndiagrammatically in FIG. 5B. In general, transmit beamformer 200A andreceive beamformer 200B may be analog or digital beamformers asdescribed, for example, in U.S. Pat. Nos. 4,140,022; 5,469,851; or5,345,426 all of which are incorporated by reference.

FIG. 7 illustrates five orthographic projection views provided by theultrasound imaging system of FIG. 1.

FIG. 7A illustrates the orthographic projection views of FIG. 7 adjustedby changing the yaw angle.

FIGS. 8, 8A, 8B and 8C illustrate introduction and use of thetransesophageal probe and the transnasal transesophageal probe forimaging of the heart.

FIGS. 9A and 9B are cross-sectional views of the human heart with theimaging probe inserted in the esophagus and an ablation catheterpositioned in the right ventricle.

FIG. 9C is a projection view of the human heart.

FIG. 9D is a projection view of the human heart including a cut-away topview displaying the ablation catheter.

FIGS. 10A, 10B and 10C are orthographic projection views collected bythe imaging probe shown in FIGS. 9A and 9B.

FIGS. 11A and 11B are cross-sectional views of the human heart with theimaging probe inserted in the esophagus and an ablation catheter in theleft ventricle.

FIG. 11C is a projection view of the human heart including a cut-awaybottom view displaying the ablation catheter shown in FIGS. 11A and 11B.

FIG. 11D is a projection view of the human heart.

FIGS. 12A, 12B and 12C are orthographic projection views collected bythe imaging probe shown in FIGS. 11A and 11B.

FIGS. 13A and 13B are cross-sectional views of the human heart with theimaging probe inserted in the esophagus and an ablation catheter locatedin the left ventricle.

FIG. 13C is a projection view of the human heart.

FIG. 13D is a projection view of the human heart including a cut-awaytop view displaying both the imaging probe and the ablation cathetershown in FIGS. 13A and 13B.

FIGS. 14A, 14B and 14C are orthographic projection views collected bythe imaging probe shown in FIGS. 13A and 13B.

Referring to FIG. 1, a transesophageal (TEE) imaging system 10 includesa transesophageal probe 12 with a probe handle 14, connected by a cable16, a strain relief 17, and a connector 18 to an electronics box 20.Electronics box 20 is interfaced with a keyboard 22 and provides imagingsignals to a video display 24. Electronics box 20 includes a transmitbeamformer, a receive beamformer, and an image generator.Transesophageal probe 12 has a distal part 30 connected to an elongatedsemi-flexible body 36. The proximal end of elongated part 36 isconnected to the distal end of probe handle 14. Distal part 30 of probe12 includes a rigid region 32 and a flexible region 34, which isconnected to the distal end of elongated body 36. Probe handle 14includes a positioning control 15 for articulating flexible region 34and thus orienting rigid region 32 relative to tissue of interest.Elongated semi-flexible body 36 is constructed and arranged forinsertion into the esophagus. Transesophageal probe 12 can be made byusing a commercially available gastroscope and the distal rigid regionshown in FIGS. 2 and 2A. The entire insertion tube is about 110 cm longand has about 30 F in diameter. The gastroscope is made, for example, byWelch Allyn (Skananteles Falls, N.Y.).

Referring to FIGS. 2 and 2A, the transesophageal imaging probe 12includes distal rigid region 32 coupled to flexible region 34 at acoupling region 40. Distal region 32 includes a distal tip housing 50for encasing an ultrasound transducer array 42, electrical connectionsand associated electronic elements. Transducer array 42 is preferably atwo-dimensional array of ultrasound transducer elements. Distal tiphousing 50 includes a lower tip housing 52 and an upper tip housing 54having a ultrasonic window 56 and a matching medium located in front oftransducer array 42. The front part of tip housing 50 has a bullet shapewith a rounded tip (or pill shape) for easy introduction into the fornixand advancement in the esophagus. Furthermore, housing 54 has a convexshape around window 56. Ultrasonic window 56 may also include anultrasonic lens and a metal foil embedded in the lens material forcooling purposes.

Transducer array 42 is bonded to an array backing 60 and the individualtransducer elements are connected to an integrated circuit 62, asdescribed in U.S. Pat. No. 5,267,221. Integrated circuit 62 is connectedto a circuit board 64 using wire bonds 66. This structure is thermallyconnected to a heat sink 68. The transesophageal probe includes twosuper flex circuits 58 and 58A, which provide connections betweencircuit board 64 and probe connector 18. The super flex circuits arearranged to have isotropic bending properties, for example, by foldinginto an accordion shape or by wrapping into a spiral shape.Alternatively, the super flex circuits may be replaced by a coaxialcable.

Alternatively, imaging system 10 may use a transnasal, transesophagealimaging probe. The transnasal, transesophageal imaging probe includes aninsertion tube connected to a distal part with a two-dimensionaltransducer array. The insertion tube is about 100 cm to 110 cm long andhas a diameter of about 10 F to 20 F. The two-dimensional transducerarray is bonded to an array backing and the individual transducerelements are connected to an integrated circuit, as described in detailabove.

FIGS. 3, 3A and 3B are schematic cross-sectional views of flexibleregion 34 of transesophageal imaging probe 12. Imaging probe 12 includesan articulation mechanism coupled to positioning control 15 (FIG. 1) forarticulating flexible region 34. Flexible region 34 exhibits torsionalstiffness and substantially no torsional play. As described below, aclinician adjusts positioning control 15 (FIG. 1) to articulate invarious ways flexible region 34 in order to position rigid distal region32 and orient transducer array 42 relative to a tissue volume ofinterest (as shown in FIGS. 8 and 8A). The clinician then can lock thearticulated flexible region 34 in place to maintain the position oftransducer array 42 during the probe manipulation or ultrasonicexamination. In a preferred embodiment, flexible region 34 includes aplurality of articulation links 71, 72 or 80 cooperatively arranged withat least one push-pull cable (or rod) controllable by positioningcontrol knobs 15. The articulation links are covered by a flexiblesheath 70.

FIG. 3 shows flexible region 34 articulated as an in-plane J hook.Flexible region 34 is made of a proximal link 71, a set of links 72(shown in detail in FIG. 3C), and a distal link 80 connected to thedistal end of highly flexible pull-push rod 74 at a connection 75.Positioning control knobs 15 control one or several rack and pinionmechanisms located in handle 14. When the rack and pinion mechanismproximally displaces push-pull rod 74, flexible region 34 bends andforms the in-plane J hook, wherein rigid distal region 32 and flexibleregion 34 are within the same plane. This in-plane bend is facilitatedby the design of articulation link 72 cooperatively arranged withpush-pull rod 74 connected to distal link 80 at its distal end.Articulation link 72 is shown in FIG. 3C.

Referring to FIG. 3C, articulation link 72 has a ring-like structurethat includes a pivotable hinge connecting two neighboring links 72. Thepivotable hinge includes two hinge pins 86A and 86B (not visible in thisperspective view) disposed on the opposite sides of link 72 andextending from recessed surfaces 88A and 88B (again not visible),respectively. Hinge lips 90A and 90B include inside surfaces 91A (againnot shown but described to illustrate the symmetry) and 91B, which havea complementary shape to the shape of surfaces 88A and 88B. Hinge lips90A and 90B also include holes 92A and 92B, respectively, which areshaped to receive the hinge pins.

Articulation link 72 also includes a stop surface 94 and a stop surface96. Stop surface 94 is positioned to provide a pre-selected maximumbending of articulation region 34, facilitated by each link, upon thepulling action of push-pull rod 74. Stop surface 96 is positioned at aheight that enables articulation region 34 to assume a straightorientation when push-pull rod 74 disposed in channel 73 does not pullon distal link 80. Alternatively, stop surface 96 is designed forarticulation region 34 to assume any selected orientation. For example,stop surface 96 may be designed for articulation region 34 to assume anopposite bend when push-pull rod 74 pushes on distal link 80.Articulation links 72 are made of a plastic or metal, such as brass orstainless steel that can also provide electrical shielding forelectrical wires located inside. The surface of articulation links 72 isdesigned to carry sheath 70 while articulation links 72 can still bendreadily without gripping or pinching sheath 70.

FIG. 3A shows distal part 30 articulated as an out-of-plane J hook.Flexible region 34 includes proximal link 71, distal link 80 and anotherset of distal links 82. Push-pull rod 74 extends in channel 73 (FIG. 3C)from a rack and pinion mechanism to a connection 75 in link 80.Push-pull rod 76 extends from a distal end 77 connected to distal link82 to another rack and pinion mechanism (not shown) near handle 14.Push-pull rod 74 is displaced proximally to bend articulation region 34.Push-pull rod 76 displaces distal link 82, connected to rigid distalregion 32; these two displacements form the out-of-plane J hook havingflexible region 34 displaced out of the plane of rigid distal region 32.

FIG. 3B shows distal part 30 articulated as an in-plane S hook. Flexibleregion 34 includes proximal link 71, sets of links 72A, an anchoringlink 84, a set of links 72, and distal link 82 connected to distal rigidregion 32. Push-pull rod 74 extends from its distal end 75, connected tolink 84, to a rack and pinion mechanism located near handle 14.Push-pull rod 78 extends from its distal end 79, connected to link 82,through links 72, link 84, links 72A and link 71 to another rack andpinion mechanism located in the catheter handle. Articulation links 72Aare basically mirror images of links 72, but include two channels foraccommodating push-pull rods 74 and 78. Links 72 enable articulation inone orientation, and links 72A enable articulation in a 180 degreesymmetric orientation. By proximally displacing push-pull rod 74, therack and pinion mechanism actuates displacement of the proximal part ofarticulation region 34 in one direction. Furthermore, by proximallydisplacing push-pull rod 78, the rack and pinion mechanism bends thedistal part of articulation region 34 in another direction, therebyforming the in-plane S hook. That is, the in-plane S hook has flexibleregion 34 and distal rigid region 32 located in the same plane.

The articulation region shown in FIG. 3B may be further modified toinclude push-pull rod 76 placed inside modified link 72 as shown in link72A. By proximally displacing push-pull rod 76, articulation region 34forms an out-of-plane S hook. The out-of-plane S hook has flexibleregion 34 located in one plane and distal rigid region 32 bend out ofthat plane. This arrangement enables both tilting transducer array 42and pulling it back to achieve a desired distance from the tissue ofinterest. A clinician manipulates the control knobs 15 until the tip ofthe probe has been articulated to a position where transducer array 42has a desired orientation relative to the tissue volume of interest.When transducer array 42 is properly positioned the physician locks thearticulation mechanism in its current position using a brake. After thearticulation mechanism is locked, the imaging system collects the echodata, as shown in FIGS. 8 and 8A.

In the preferred embodiment, the TEE imaging system or the transnasalTEE imaging system includes a transmit beamformer, a receive beamformer,an image generator, a surface detector (or a boundary detector), and animage display, all of which are shown diagrammatically in FIGS. 5through 5C. The system generates several novel orthographic views thatutilize planar imaging and projection imaging techniques. Theacquisition of the images is first described in connection with FIG. 4.FIG. 4 shows a scanned volume V of data (i.e., an image volume)collected by transducer array 42. Transducer array 42, controlled by atransmit beamformer 200A (described in connection with FIG. 5B), emitsultrasound lines over an azimuthal angular range for a selectedelevation angle φ. Transducer array 42 detects echoes timed by a receivebeamformer 200B (described in connection with FIG. 5B) over a selectedscan range (R) and an azimuthal angular range (θ=±45°) to acquireultrasound data for one image plane, e.g., S₀, shown in FIG. 4. To imagethe tissue volume V, the imaging system collects data over several imageplanes (called 2D slices or image sectors) labeled as S⁻¹, S⁻², S⁻³, S₀,S₁, S₂ and S₃, distributed over an elevational angular range (φ=±30°).

FIGS. 4A through 4E show examples of different orientations of thescanned volumes collected by imaging probe 12 having the probearticulations described in connection with FIGS. 3 through 3C.Specifically, FIG. 4A shows an imaging volume 100 collected by imagingprobe 12 having flexible region 34 extended straight. The imaging systemcollects the echo data over several image planes S⁻¹, S⁻², S⁻³, S₀, S₁,S₂ and S₃ described above. FIG. 4B shows a scanned volume 102 collectedby the imaging system having flexible region 34 articulated in the formof the in-plane J hook, shown in FIG. 3. The J hook can be articulatedin the anterior, as shown in FIG. 4B, direction or the posteriordirection and can also be displaced out-of-plane, as described inconnection with FIG. 3A. FIG. 4C shows a scanned volume 104 generated bythe imaging system with flexible region 34 articulated in the form ofthe out-of-plane J hook. FIGS. 4D and 4E depict scanned volumes 106 and108 generated by the imaging system when flexible region 34 isarticulated as in-plane and out-of-plan S hooks.

FIGS. 5, 5A and 5B show diagrammatically the imaging system according toa presently preferred embodiment. The entire operation of the imagingsystem is controlled by a control processor 140, shown in FIG. 5A.Control processor 140 receives input commands from input controls 142through 167 and provides output control signals 170 through 191. Controlprocessor 140 provides control data to a beamformer 200, and providesimage control data to image generator 250, which includes processing anddisplay electronics. Beamformer 200 includes a transmit beamformer 200Aand a receive beamformer 200B, shown diagrammatically in FIG. 5B. Ingeneral, transmit beamformer 200A and receive beamformer 200B may beanalog or digital beamformers as described, for example, in U.S. Pat.Nos. 4,140,022; 5,469,851; or 5,345,426 all of which are incorporated byreference.

According to one embodiment, transducer array 42 is preferably atwo-dimensional array of ultrasound transducer elements that can bearranged into groups of elements (i.e., sub-arrays) usingelectronically-controllable switches. The switches can selectivelyconnect transducer elements together to form sub-arrays having differentgeometrical arrangements. That is, the two-dimensional array iselectronically configurable. The switches also connect the selectedconfiguration to transmit beamformer 200A or receive beamformer 200Bshown in FIG. 5B. Each geometrical arrangement of the transducerelements is designed for optimization of the transmitted ultrasound beamor the detected receive beam.

Transducer array 42 may be fabricated using conventional techniques asdescribed, for example, in U.S. Pat. No. 5,267,221 issued Nov. 30, 1993to Miller et al. The transducer elements may have center-to-centerspacings on the order of 100-300 micrometers. The sizes of thetransducer elements and the spacings between the transducer elementsdepend on the transducer ultrasound frequency and the desired imageresolution.

Referring to FIG. 5B, the imaging system includes transducer array 42with designated transmit sub-arrays 43 ₁, 43 ₂, . . . , 43 _(M) anddesignated receive sub-arrays 44 ₁, 44 ₂, . . . , 44 _(N). Transmitsub-arrays 43 ₁, 43 ₂, . . . , 43 _(M) are connected to intra-grouptransmit pre-processors 210 ₁, 210 ₂, . . . , 210 _(M), respectively,which in turn are connected to transmit beamformer channels 215 ₁, 215₂, . . . , 215 _(M). Receive sub-arrays 44 ₁, 44 ₂, . . . , 44 _(N) areconnected to intra-group receive pre-processors 220 ₁, 220 ₂, . . . ,220 _(N), respectively, which in turn are connected to receivebeamformer channels 225 ₁, 225 ₂, . . . , 225 _(N). Each intra-grouptransmit pre-processor 210 _(i) includes one or more digital pulsegenerators that provide the transmit pulses and one or more voltagedrivers that amplify the transmit pulses to excite the connectedtransducer elements. Alternatively, each intra-group transmitpre-processor 210 _(i) includes a programmable delay line receiving asignal from a conventional transmit beamformer. For example, thetransmit outputs from the commercially available ultrasound system HPSonos 5500 may connected to the intra-group transmit pre-processors 210_(i) instead of the transducer elements done presently for HP Sonos 5500(both previously manufactured by Hewlett-Packard Company, now AgilentTechnologies, Inc., Andover, Mass.).

Each intra-group receive pre-processor 220 i may include a summing delayline, or several programmable delay elements connected to a summingelement (a summing junction). Each intra-group receive processor 220_(i) delays the individual transducer signals, adds the delayed signals,and provides the summed signal to one receive beamformer channel 225_(i). Alternatively, one intra-group receive processor provides thesummed signal to several receive beamformer channels 225 _(i) of aparallel receive beamformer. The parallel receive beamformer isconstructed to synthesize several receive beams simultaneously. Eachintra-group receive pre-processor 220 _(i) may also include severalsumming delay lines (or groups of programmable delay elements with eachgroup connected to a summing junction) for receiving signals fromseveral points simultaneously, as described in detail in U.S. Pat. No.5,997,479, which is incorporated by reference.

Control processor 140 provides delay commands to transmit beamformerchannels 215 ₁, 215 ₂, . . . , 215 _(M) via a bus 216 ₁ and alsoprovides delay commands to the intra-group transmit pre-processors 210₁, 210 ₂, . . . , 210 _(M) via a bus 211. The delay data steers andfocuses the generated transmit beams over transmit scan lines of aselected transmit pattern, as shown for example in FIGS. 6 through 6C.Control processor 140 also provides delay commands to receive beamformerchannels 225 ₁, 225 ₂, . . . , 225 _(N) via a bus 226 and delay commandsto the intra-group receive pre-processors 220 ₁, 220 ₂, . . . , 220 _(N)via a bus 221. The applied relative delays control the steering andfocussing of the synthesized receive beams. Each receive beamformerchannel 225 i includes a variable gain amplifier, which controls gain asa function of received signal depth, and a delay element that delaysacoustic data to achieve beam steering and dynamic focusing of thesynthesized beam. A summing element 230 receives the outputs frombeamformer channels 225 ₁, 225 ₂, . . . , 225 _(N) and adds the outputsto provide the resulting beamformer signal to image generator 250, shownin detail in FIGS. 5(1)-5(5). The beamformer signal represents onereceive ultrasound beam synthesized along one receive scan line.

According to another embodiment, transducer array 42 includes a largernumber of elements wherein only selected elements are connected to theintegrated circuit. Transducer array 42 has the individual transducerelements arranged in rows and columns. The electronically-controllableswitches selectively connect the elements adjacent in the rows andcolumns. Furthermore, the array may also includeelectronically-controllable switches for selectively connectingadjacent, diagonally-located transducer elements. The selectedtransducer elements can be connected to the transmit or receive channelsof the imaging system such as HP Sonos 5500 or the system describedbelow. A T/R switch connects the same groups of elements alternativelyto the transmit or receive channels. The connections may be direct ormay be indirect through one or more other transducer elements.

By appropriately connecting the elements into groups and phasing theelements by the transmit beamformer, the generated ultrasound beam istransmitted along a desired scan line and is focused at a desired depth.Various transducer connections are described in U.S. patent applicationSer. No. 09/044,464, filed on Mar. 19, 1998, which is incorporated byreference. For example, the transducer elements may be connected incolumns together by closing neighboring column switches. Each column isthen connected via one selected transducer element of a selected row toa different system channel, as shown in FIG. 5B. The phased transducerelements then form an imaging plane that is perpendicular to the planeof the array and is vertical (i.e., parallel to the selected column).The elevation direction is horizontal, as shown in FIG. 4.

However, the imaging system can generate the scanned volume V by theimage planes (S⁻¹, S⁻², S⁻³, S₀, S₁, S₂ and S₃) oriented arbitrarilyrelative to the transducer rows and having columns. For example,transducer elements in different rows and columns are interconnected tosystem channels to provide imaging in a plane that is oriented at anangle with respect to the transducer rows and columns. For example, thetransducer elements of neighboring rows and columns are connected to thebeamformer in a step-like pattern. This configuration provides theimages parallel to a plane that is oriented at about 45 degrees withrespect to the column orientation. In another embodiment, the transducerelements are connected the beamformer to form approximately circularcontours. This improves the elevation focus control. The acoustic centercan be placed on any element that is connected to a system channel. Ingeneral, the transducer configurations can be combined with theelevation focus control by determining the appropriate equal delaycontours and connecting elements along those contours.

The imaging system acquires the echo data over a selected size of thevolume V by executing a selected scanning pattern. FIG. 6 shows a 100%rectangular scanning pattern 240 performed, for example, by collectingthe echo data over several image planes (2D slices) S⁻¹, S⁻², S⁻³, S₀,S₁, S₂ and S₃, as described in connection with FIG. 4. However, toreduce the scanning time, the imaging system can perform data scans overa reduced volume centered on the tissue region of interest. For example,FIG. 6A shows an elliptical scanning pattern 242, which includes about70% of the scan lines used in the rectangular scanning pattern 240,shown in FIG. 6. FIG. 6B shows a diamond-shaped pattern 244 ₁ whichincludes only about 50% of the scan lines, and FIG. 6C shows astar-shaped pattern 246, which includes only about 25% of the scanlines.

Referring also to FIG. 7, the imaging system can generate and displayseveral unique views that are within two orthogonal central planes S₀and L₀ (FIG. 4) having a zero degree azimuthal and elevational location,respectively. The generated views include projection images that aregenerated over the region of interest or over the entire area of the 2Dslice. Specifically, when the plane S₀ (having the elevation angle φ=0°)is imaged from y=∞ toward y=0, it is called a front projection view 286.A rear projection view (not shown in FIG. 7) is imaged from y=−∞ towardy=0. The image sectors located at L₀ (having the azimuthal angle θ=0°)imaged from x=∞ toward x=0 and x=−∞ toward x=0 are called a right sideprojection view 292 and a left side projection view 291, respectively.The imaging system can generate and display a top projection view 337,which is a modified C-scan image of a selected tissue surface imagedfrom z=0 to z=∞. The location of modified C-scan image can bepre-selected, defined in the plane views (image planes), or defined inthe front or side projection views, as shown in FIG. 7. The imagingsystem also generates and displays a bottom projection view 336, whichis a modified C-scan image of the tissue surface imaged from z=∞ to z=0.In general, however, the projection direction does not have to beparallel with the x, y or z axes, but may be any direction selected by aclinician.

The imaging system is designed to provide images that are easilyunderstandable to a clinician. As shown in FIG. 7, the image displaypositions the front projection view (286) in the center, the left sideprojection view (291) on the left-hand side, and the right sideprojection view (292) on the right-hand side of the front projectionview. Furthermore, the image display displays the top projection view(337) above the front projection view, and the bottom projection view(336) below the front projection view. Next to each view there is adisplay icon. Display icons 370, 372, 374, 376 and 378 provide theorientation and provide the scan range of the associated views 286, 291,292, 337 and 336, respectively. The clinician can select and re-selectthe scan parameters and the display parameters based on the informationprovided in the individual views and the display icons. The system willthen generate new views and the associated display icons, as describedbelow.

FIG. 7A shows the novel orthographic views of FIG. 7 recalculated for ayaw angle of 30 degrees. The left side projection view 291A and theright side projection view 292A correspond to the left side projectionview 291 and the right side projection view 292 (FIG. 7), respectively.The left side view icon 372A, and the right side view icon 374A show thenew display regions after recalculating the yaw angle. Similarly, thetop view icon 376A and the bottom view icon 378A display the yaw angleto a clinician.

Importantly, the imaging system can generate the projection images overthe entire area of a plane view or over a region of interest defined bya clinician after viewing an acquired plane view (i.e., 2D slice image).If the projection images are generated only over the region of interest,than each image includes a projection view within the region of interestand plane view (2D slice) outside the region of interest. Specifically,the right side view includes the right side projection view within theregion of interest and a plane view at the plane L₀. Similarly, the leftside view includes the left side projection view within the region ofinterest and the plane view at the plane L₀. That is, views 291 and 292(or 291A and 292A) differ only within the region of interest, where theleft side projection view and the right side projection view aregenerated and displayed, and are identical outside the region ofinterest.

The imaging system initially provides the front view and the side viewsto a clinician. The imaging system also provides at least one modifiedC-scan image that is an image of a selected surface perpendicular to thefront and side view planes over the scanned volume, V. A clinician canmanually select (or the system can select automatically) the surface tobe shown in the modified C-scan image. The imaging system generatesthese orthographic projection views in real time, at a frame rate above15 Hz (and preferably above 20 Hz, or in the range of about 30 Hz to 100Hz).

Referring again to FIGS. 5, 5A and 5B, the imaging system includestransmit beamformer 200A and receive beamformer 200B, control processor140, image generator 250 that includes the surface or boundary detector,and the image display. Control processor 140, shown in FIG. 5A, providesthe control data, such as timing 170, a scan line number 171 and a range175, to beamformer 200 to control scanning within an image sector. Inanother embodiment, transmit beamformer 200A phases the transmissionfrom the transducer elements to emit the ultrasound beam along severaltransmit scan lines spaced over a selected angular distribution in apie-shaped sector. In the receive mode, receive beamformer 200B phasesthe transducer elements to detect the ultrasound echoes along one orseveral receive scan lines spaced over a selected angular distribution.The operation of the transmit and receive beamformers connected to aphased array is described, for example, in U.S. Pat. Nos. 4,140,022;4,893,283; 5,121,361; or 5,469,851.

To define parameters of the B-scan, control processor 140 receives inputdata defining a sector scan depth 148, a frame rate 150, and anazimuth/elevation scan ratio 152. The sector scan depth defines the scanrange (R) over which the echoes are detected, for example, 4centimeters, 8 centimeters, or 10 centimeters, depending on the locationof the transducer array relative to the biological tissue of interest.The clinician can select frame rate 150 depending on the tissuestructures of interest. For real-time images of a moving organ, theframe rate has to be at least several frames per second to avoidblurring of the image due to the movement of the tissue. The user alsoselects azimuth/elevation scan ratio 152, which varies the B-scan from alarge azimuth scan (i.e., a large angular range of the scan lines withinimage sector) of a single sector to a minimum azimuth scan performedover a large number of sectors (i.e., a small angular range for eachsector scanned over a large elevation displacement.) Thus,azimuth/elevation scan ratio 152 provides a bottom view image aspectratio (i.e. x/y dimension) of bottom view 336 and a top view aspectratio of top view 337 for the C-scan, as shown in FIG. 7.

Depending on the preferred sector scan depth, the frame rate, and theazimuth/elevation scan ratio, control processor 140 calculates theangular spacing between the scan lines and the number of scan lines(171) for each sector. Based on the initial values, processor 140allocates the largest possible number of scan lines and the largestpossible number of sectors. Specifically, processor 140 calculates theangular spacing between the scan sectors, that is, a sector angle (173)and the number of sectors (174). Control processor 140 provides thesevalues to beamformer 200.

Control processor 140 selects the scanning sequence performed bybeamformer 200. The transmit beamformer directs emission of the phasedultrasound beam along the scan lines over the ranges calculated for eachsector. For each emitted scan line, the receive beamformer phases thetransducer elements to detect the ultrasound echoes along acorresponding receive scan line. Alternatively, the receive beamformersynthesizes the scan data from several receive scan lines that arespaced over a selected angular distribution as is described, forexample, in the U.S. Pat. No. 5,976,089, entitled “Increasing the FrameRate of a Phased Array Imaging System,” which is incorporated byreference. The RF data is filtered by a filter with a pass band of asmuch as 60% around the center frequency of as high as 10 MHz, orpreferably a pass band of about 35% around the center frequency in therange of about 5 MHz to 7 MHz.

Control processor 140 receives a time gain compensation (TGC) input 142,a lateral gain compensation (LGC) input 144, and an elevation gaincompensation (EGC) input 146 entered by a clinician or stored in amemory. The TGC control adjusts the receive channel gain, usually indiscrete steps, as a function of the distance from the transducer array.The TGC control compensates for attenuation of ultrasound waves as theypropagate through the medium. The LGC control varies the receive channelgain as a function of the azimuthal displacement of a particular scanline, while the gain along the scan line remains unaffected with thedistance from the transducer array. The LGC control is desirable wherethe ultrasound signal decreases in a particular region due to theanatomical structure of the tissue, or where tissue orientation in thesubject results in echo signals having varying brightness. The EGCcontrol varies the receive channel gain as a function of the elevationaldisplacement, i.e., adjusts the gain for a selected scan sector (i.e.,scan plan). The user can also re-adjust the TGC, LGC and EGC manually sothat the image “looks” better.

Referring to FIGS. 5(1)-5(5), the receive beamformer 200B providesdetected RF echo signals to the image generator that includes a timegain compensator (TGC) 262, a lateral gain compensator (LGC) 264, and anelevation gain compensator (EGC) 266, which perform the correctionsdescribed above. The EGC 266 provides the compensated data to a B-scansignal processor 272, a C-scan signal processor 315, and boundarydetectors 302 and 322.

Alternatively, the TGC 262, the LGC 264 and the EGC 266 are replaced bya rational gain compensation (RGC), which is described in U.S. Pat. No.5,195,521 and in “Rational Gain Compensation for Attenuation in CardiacUltrasonography,” Ultrasonic Imaging, Vol. 5, pp. 214-228 (1983). TheRGC compensates for attenuation while distinguishing between blood andcardiac tissue. The RGC varies the signal gain for blood and cardiactissue by using a threshold value below which the backscattered signalis defined as “zero.” In this case, the backscattered signal is arrivingfrom blood.

Referring still to FIGS. 5(1)-5(5), the image generator includes postprocessors 276 and 318, which receive filtered and compensated data fromenvelope detectors 274 and 317. Post processors 276 and 318 control thecontrast of each data point by mapping the data onto a set of selectedcurves. After assigning a contrast level to each data point, a scan linebuffer may be used to hold temporarily the data for one scan line.

The image generator includes a scan line data volume memory 278 and aboundary data volume memory 280. Scan line data volume memory 278receives the processed echo data and also receives from processor 140display line number 172, sector number 174, and range 175. Data volumememory 278 stores the data in a matrix form by assigning a number toeach sector and another number to each scan line in the azimuthaldirection. The size of the data matrix stored in data volume memory 278depends upon the acoustic frame rate. Each scan cycle (i.e., acousticframe) fills the data matrix with the data acquired over the scan volumedelineated by the azimuthal range and the elevation range. The scan linenumber corresponds to the column number in the data volume matrix. Thesector number corresponds to the row number in the data volume matrix.The scan range data corresponds to the column height in the data volumematrix. Data volume memory 278 provides its output 279 to viewprocessors 285 and 290.

Boundary data volume memory 280 also receives the processed echo dataand data from a majority vote processor 308. Boundary data volume memory280 also receives from processor 140 display line number 173, sectornumber 174, range 175 and B-scan surface contrast 179. Data volumememory 280 also stores the data in a matrix form. Data volume memory 280provides its output 281 to view processors 285 and 290.

Azimuthal view interpolation processor 285 and an elevation viewinterpolation processor 290 receive data from memory 278 and memory 280and receive data from B-scan edge indicator 310 and C-scan edgeindicator 330. Depending on the view input, interpolation processors 285and 290 generate the selected front view and the selected side view,respectively. The front and side views are provided to a display planememory 300 which in turn provides a video signal 350 to a video display.Based on the B-scan data, a clinician can select a region that includesa selected tissue region. The clinician selects the tissue of interesteither by setting range gates or by drawing a region of interest (ROI)around the imaged tissue.

The imaging system is designed for automatic operation or interactionwith a clinician. A clinician can outline the region of interest bylooking at the front plane view or the side plane view (i.e., the B-scanimages). Based on the outline (or another input), control processor 140transforms an ROI perimeter input 153 into a range 175, ROI markers andgates 176. They can be displayed on the video display to outline aregion. They are also provided to boundary detector 302 and boundarydetector 322 to perform surface (boundary) detection in response toechoes from points within the ROI. Thus, the surface detector (i.e., atleast one of boundary detectors 302 or 322) enables the creation of aprojection image region, within the ROI perimeter, and thus the surfacedetector enables surface visualization.

It is important to note that a tissue surface or a tissue structureusually undulates in and out of a single plane view or even a range ofviews. Several prior art ultrasound systems can display echo data onlyin the form of 2D slices or planes. Such plane views may provide imagesthat have a random patchwork of areas. The present invention recognizedthat a clinician may find it difficult to visualize or understand suchplane view images, particularly when the transducer array is notcompletely aligned with a surface of interest. To eliminate thisproblem, the present imaging system utilizes planar imaging andprojection imaging for visualizing tissue surfaces and in generalthree-dimensional anatomical structures (including therapy devices,diagnostic devices, corrective devices, stents etc.) inside a patient.

As shown in FIGS. 5(1)-5(5), B-scan boundary detector 302 includes asignal processor 304, a tissue indicator 306, a majority vote processor308, and an edge indicator 310. U.S. Pat. No. 5,195,521, which isincorporated by reference, discloses a majority vote circuit andcircuits for generating the ROI. Control processor 140 provides toboundary detector 302 ROI enable output 176, line number output 171, andsector number output 174. signal processor 304 derives from the RF dataa characteristic sensitive to the difference between the echo fromtissue and from blood in order to increase the accuracy of locating thetissue boundary. The characteristic is the amplitude of integratedbackscatter from tissue and from blood. Signal processor 304 determinesthe amplitude of the integrated backscatter and provides it to tissueindicator 306. (Alternatively, tissue indicator 306 may receive the echoRF data directly.)

Tissue indicator 306 outputs a signal that is equal to either one orzero depending on whether the echoes are from tissue or blood. Majorityvote processor 308 determines whether the majority of the signals arezero or one for the individual scan lines within a scan sector. That is,majority vote processor 308 produces, at each range, a signal indicativeof whether the signal provided by the tissue indicator 306 representsechoes from tissue or blood. Majority vote processor 308 produces thissignal for a majority of consecutive scan lines including the linecurrently being scanned. If indicator 306 outputs for a majority of thelines a signal indicating that reflections at a range are from tissue,majority processor 308 outputs a signal indicative of the fact that thereflections are from tissue. Similarly, if tissue indicator 306 outputsa different signal for a majority of lines, majority vote processor 308outputs another signal indicative of the fact that the reflections arefrom blood.

Edge indicator 310 responds to a change in the signal provided bymajority vote processor 308 to produce short pulses that are used toform an outline of cavities or ventricles in the image. Specifically,edge indicator 310 includes an edge indicator circuit (disclosed in U.S.Pat. No. 5,195,521) that outputs a high logic level for, e.g., 1microsecond whenever the output of majority vote processor 308 changesfrom a high level to a low level and vice versa. The output 312 fromedge indicator 310 is provided to processors 285 and 290 forhighlighting B-scan borders. Furthermore, the output 309 from majorityvote processor 308 is provided to boundary data volume memory 280 asdescribed above.

C-scan boundary detector 322 operates similarly as B-scan boundarydetector 302. C-scan boundary detector 322 includes a signal processor324, a tissue indicator 326, a majority vote processor 328, and an edgeindicator 330. Control processor 140 provides to boundary detector 322 arange gate enable output 177, line number output 171, and sector numberoutput 174. Signal processor 324 derives from the RF data the amplitudeof integrated backscatter from tissue and from blood and provides it totissue indicator 326. Tissue indicator 326 outputs a signal that isequal to either one or zero depending on whether the echoes are fromtissue or blood. Majority vote processor 328 determines whether themajority of the signals are zero or one for the individual scan lineswithin a scan sector. That is, majority vote processor 328 produces, ateach range, a signal indicative of whether the signal provided by thetissue indicator 326 represents echoes from tissue or blood.

As described for edge indicator 310, edge indicator 330 responds to achange in the signal provided by majority vote processor 328 to produceshort pulses that are used to form an outline of cavities or ventriclesin the image. Specifically, edge indicator 330 outputs a high logiclevel whenever the output of majority vote processor 328 changes from ahigh level to a low level and vice versa; that is, the detected echoeschange from tissue to blood and vice versa. The output 332 from edgeindicator 330 is provided to processors 285 and 290 for highlightingC-scan borders. Furthermore, the output 329 from majority vote processor328 is provided to a gated peak detector 320.

Referring to FIG. 5C, gated peak detector 320 provides the C-scan datathat follow a selected tissue surface located within the selected ROI orrange. A sampler 352 receives output 319 from post-processor 318 andprovides the sampled data to a hold circuit 356 and to a delay circuit360. Furthermore, the output 329 of majority vote processor 328 isprovided to a positive trigger comparator 354 and to a negative triggercomparator 358. When majority vote processor 328 detects the proximaltissue surface, positive trigger comparator 354 provides an enablesignal to hold circuit 356, which in turn provides its output 357 to aproximal/distal surface circuit 364.

A clinician selects the top view or the bottom view using input 162, andcontrol processor 140 provides a proximal/distal surface output 184 toproximal/distal surface circuit 364, which functions as a switch. Whenmajority vote processor 328 is detecting the distal surface, negativetrigger comparator 358 provides an enable signal to a hold circuit 362,which in turn provides its output 363 to proximal/distal surface switch364. Proximal/distal surface switch 364 receives a proximal/distalsurface value 184 from control processor 140. Depending on theproximal/distal surface output 184, proximal/distal switch providessignal 357 or signal 363 to a yaw adjustment processor 335 and, in turn,to contrast adjustment processor 340. That is, proximal/distal switch364 determines whether gated peak detector 320 sends the large valuefrom the positive-going edge of the RF signal, or sends the large valuefrom the negative going edge of the RF signal. In this way, the systemgenerates the data for the top view or the bottom view (both beingmodified C-scan images).

As described above, gated peak detector 320 selects the proximal ordistal surface data from the RF signal and sends it to yaw adjustmentprocessor 335. For a zero degree adjustment (i.e., yaw adjustment output183 equal to zero), the data is provided unchanged to a contrastadjustment processor 340. Contrast adjustment processor 340 achieves aseparate contrast adjustment for the bottom view and the top view (i.e.,the two C-scan images). A clinician provides a C-scan contrast input156, which control processor 140 provides as C-scan output 178. Forexample, a tissue wall may be seen on the front and side views (theB-scan cross-sections) as a white line, but a clinician may want to seeit in gray to look for landmarks, lesions or therapy devices in thebottom view. The C-scan contrast creates realistic tissue surfaceappearance. After the contrast adjustment, contrast adjustment processor340 provides the contrast adjusted data to a scale adjustment processor345. Scale adjustment processor 345 maps the contrast adjusted data tothe scale used for the front and side views (i.e., B-scan images) andprovides the data to video display memory 300.

The ultrasound imaging system 10 provides six degrees of freedom forobtaining and adjusting the image. The electronic adjustment providesthree degrees of freedom to obtain a selected view orientation. Threeadditional degrees of freedom come from the spatial orientation oftransducer array 42 relative to a selected tissue structure. Transducerarray 42 is oriented by articulating articulation region 34 as shown inFIGS. 3 through 3B. The articulation alters orientation of the scannedvolume and thus the orientation of the front, side, and bottom views, asshown in FIGS. 4A through 4E. Image generator 250 provides predictableand easily understandable views of three-dimensional tissue structures.

The orthographic projection views 286, 291 and 292 can be electronicallyrepositioned by providing new input values to control processor 140.After viewing the front view 286 (or the rear view) and the side views291 or 292, a clinician can electronically change, or reposition thescanned volume V by entering new values for scan sector depth 148, framerate 150, or azimuth-to-elevation scan ratio 152 to perform anotherscan. Alternatively, the clinician can re-select the imaged tissue bychanging a pitch offset 158 or a roll offset 159 of the new scan. Thepitch offset changes the scan lines in the azimuthal direction. The rolloffset changes the elevation of a line relative to transducer array 42and thus changes the position of the individual image sectors, shown inFIG. 4. This way the clinician can direct a scan over a smaller datavolume centered on the tissue of interest. By scanning over the smallervolume, the system improves real-time imaging of moving tissue byincreasing the frame rate, because it collects a smaller number of datapoints. Alternatively, the system collects the same number of datapoints over the smaller volume to increase the resolution.

The imaging system 10 uses several icons to provide understandableimages. Referring to FIGS. 5(1)-5(5), 5A(1)-5A(2) and 7, an azimuthalicon generator 289 receives a pitch adjustment 181 and provides data fordisplaying a front azimuthal icon 370 for the front view (or a rearazimuthal icon for the rear view). An elevation icon generator 299receives a roll adjustment 182 and provides data for displaying a leftelevation icon 372 (shown in FIG. 7) for the left view 291 and a rightelevation icon 374 for the right view 292. A yaw icon generator 346receives a yaw adjustment 183 and provides data for displaying a topicon 376 and a bottom icon 378 showing the yaw orientation (FIG. 7). Aclinician uses the icons for better understanding of the images.Furthermore, a clinician uses the icons to steer and direct the acousticbeam to a selected value of interest or to locate and orient the imagesrelative to the orientation of transducer array 42.

The imaging system 10 can also vary electronically the presentation ofthe orthographic projection views (i.e., the front, rear, side, top, andbottom views). After viewing the front view and the side views (shown inFIG. 7), a clinician can change the orientation of the views by changinga yaw offset 160. Yaw output 183 is provided to processors 285, 290 and335, which re-calculate the front, side, top and bottom views. Therecalculated front view 286A, left side view 291A, right side view 292A,top view 337A and bottom view 336A are shown in FIG. 7A. Furthermore,azimuthal icon generator 289 provides data for displaying front viewazimuthal icon 370A, and elevation icon generator 299 provides data forboth left view elevation icon 372A and right view elevation icon 374A.Yaw icon generator 346 provides data for displaying both top view icon376A and bottom view icon 378A.

The yaw adjustment usually requires interpolation to generate new planesof scan lines. These are generated from the nearest set of scan linesusing the data volume matrix to create the new data planes (i.e.,sectors). This interpolation process uses the same principle as the scanconversion process performed by real-time 2D systems that convert thepolar coordinate data into the rectangular coordinate data used for thedisplay (see, e.g., U.S. Pat. No. 4,468,747 or U.S. Pat. No. 5,197,037).Each re-calculated data plane can be stored in a memory associated withprocessors 285 and 290. The recalculated data planes are provided tovideo display plane memory 300 and then to a video monitor by signal 350(shown in FIG. 5). Scan converters 288 and 298 convert the ultrasounddata, acquired in R, theta, into an XY format for both the azimuth andelevation planes. Scan converters 288 and 298 are constructed asdescribed in U.S. Pat. No. 4,468,747; U.S. Pat. No. 4,471,449; or U.S.Pat. No. 5,197,037, or “Ultrasound Imaging: an Overview” and “A ScanConversion Algorithm for Displaying Ultrasound Images”, Hewlett-PackardJournal, October 1983.

Importantly, the entire system provides six degrees of freedom toacquire and generate high quality images. Imaging probe 12 providesthree degrees of freedom in positioning transducer array 42 relative tothe examined tissue. By articulating, rotating and displacing distalpart 30, a clinician maneuvers transducer array 42 to a selectedposition and orients array 42 relative to the examined tissue. Theimaging electronics provides another three degrees of freedom forgenerating the images by selecting the pitch, roll and yaw values. Thedisplay system can generate new (re-oriented) images for different yawvalues from the collected scan data stored in the memory. The displayformat is always predictable from one position (or range of positions)to another and is easily understood by a clinician, as described below.A clinician will understand the three-dimensional structure (in time)due to the novel probe design of the TEE or transnasal TEE probe, andthe novel display system that provides anatomically correct orientationof the images. The novel probe design has the centerline of transducerarray 42 located at the apex of the pie shaped image shown in FIGS. 9Athrough 14C.

Referring to FIG. 8, prior to collecting the data, a clinicianintroduces the transesophageal probe with an introducer 135 through themouth 130, laryngopharynx 132 into the esophagus 380. After moving theprobe and the introducer past uvula 133, distal part 50 of the probe ispositioned inside the GI track at a desired location. Distal part 50with transducer array 42 may be positioned inside the esophagus, asshown in FIG. 8B, or the fundus of the stomach, as shown in FIG. 8C. Toimage the heart, the transmit beamformer focuses the emitted pulses atrelatively large depths, and the receive beamformer detects echoes fromstructures located 10-20 cm away, which is relatively far in rangecompared to the range used in, for example, an intravascular catheterintroduced into the heart.

Alternatively, as shown in FIG. 8A, a clinician introduces thetransnasal transesophageal probe with a nasotrumpet introducer 136 intothe left nostril 134 (or into the right nostril) and moves themposteriorly in the nasal pharynx, past the uvula 133, into the esophagus380. Nasotrumpet introducer 136 has a relatively large inner diameterwith relatively thin pliable walls. During the introduction procedure,the transnasal TEE probe may support the sheathing of nasotrumpetintroducer 136. Both members are curved to the anticipated internalgeometry of the patient's nasopharyngeal airways. After introduction,the transnasal TEE probe is moved down in the esophagus 380 and thedistal end with the transducer array are positioned at a desiredlocation inside the GI tract.

Similarly as for the TEE imaging probe, the transducer array of thetransnasal TEE probe is positioned inside the esophagus (FIG. 8B) or inthe fundus of the stomach 381 (FIG. 8C) and oriented to image the tissueof interest. In each case, the imaging system generates several noveltypes of images. The imaging system is particularly suitable for imagingnear tissue using near in range field because of its ability to providereal time imaging of moving organs such as the heart.

Referring to FIGS. 8B and 8C, the imaging probe can image a medicaldevice, such as a balloon catheter or an ablation catheter, introducedinto the heart. An ablation catheter 400 (for example, a cathetermanufactured by Medtronics, Inc., Sunnyvale, Calif.) is introduced intothe left ventricle 394 having its distal part 402 located near or on aninterior surface of the myocardium 399. The clinician will understandthe three-dimensional structure (in time) due to the novel design of theprobe, as described above. A novel display system provides anatomicallycorrect orientation of the orthographic projection views described inFIGS. 7 and 7A.

FIG. 9A is a cross-sectional view of the human heart along its longaxis, and FIG. 9B is a cross-sectional view along the short axis of theheart. FIGS. 9A through 9D are not displayed on the video display of theimaging system, but are provided here for explanation. Both FIGS. 9A and9B show distal part 30 of probe 12 (shown in FIGS. 1 and 2) locatedinside into the esophagus 380 (FIG. 8B) and a distal part 402 of anablation catheter 400 also located inside the right ventricle 386.

The imaging system uses transducer array 42 to collect the echo data andprovides there orthographic views (i.e., views having generallyperpendicular orientation with respect to each other), shown in FIGS.10A, 10B and 10C. The three orthographic views are a front view 420, aleft side view 450, and a top view 470, which are generated as planeviews with projection views inside the regions of interest or the rangeof interest. The video display of the imaging system displays eachorthographic projection view and an associated icon, as explained inconnection with FIGS. 7 and 7A. In the following description, we use thestandard definitions of projection views as provided, for example, inEngineering Drawing and Geometry, by R. P. Holster and C. H. Springier,John Wiley & Sons, Inc., 1961.

Referring to FIG. 9A, transducer array 42, operating in a phased arraymode, collects the echo data over an azimuthal angular range delineatedby lines 412 and 413 and a range distance 414. FIG. 10A shows thecorresponding front view 420 and a front view icon 430. Front view icon430 includes an array axis 432 and shows a front view field 434corresponding to the azimuthal angular range. Array axis 432 shows thelongitudinal axis of transducer array 42 for a selected value of yawadjustment 243 (FIG. 7A). In FIG. 10A, front view 420 shows distal part402 of ablation catheter 400 positioned on the proximal surface (topsurface) 389 of the septum 388, which separates the right ventricle 386and the left ventricle 394 (shown in FIG. 9A). Front view 420 alsopartially shows the aortic valve 395 between the left ventricle 394 andthe aorta 396. A clinician can set the location of gates 416 and 417 andan ROI marker 415.

Referring to FIGS. 9B and 10B, the imaging system can also generate aleft side view 450 by collecting echo data over a selected elevationangular range delineated by lines 445 and 446 and an ROI marker 448.Transducer array 42 (FIG. 9A) collects echo data over a selected numberof image sectors, wherein a line 447 indicates the location of the frontview plane. Left side view 450 displays a portion of the left ventricle394, the right ventricle 386, the septum 388, and distal part 402 ofcatheter 400, located on the right ventricular surface 389 of the septum388. Referring still to FIG. 10B, left side view icon 460 shows anavailable side view field 462 and an elevation angular range 464, overwhich the image sectors were acquired.

FIGS. 9C and 9D are projection views of the human heart. FIG. 9D shows acut-away top view displaying distal part 402 of the ablation catheterand the surface 389 of the septum 388 within the ranges (i.e., gates 416and 417) defined in FIGS. 9A and 9B. The corresponding FIG. 10C displaysa C-scan projection, top view 470, generated from the B-scan data withinrange gates 416 and 417, and displays a top view icon 490. Top view 470shows distal part 402 of catheter 400 placed on the proximal surface 389of the septum 388. Range gates 416 and 417 and angular range lines 412,413, 445, and 446 define the area of top view 470. The area of top view470 is not identical to the shaded area due to the curvature of theproximal surface 389 of the septum 388. FIG. 10C also displays top viewicon 490, which includes a rectangular array 492 and an array axis 494.The angle of axis 494 relative to the side of rectangular area 492indicates the yaw angle of top view 470, wherein the yaw angle is zeroin this case.

FIGS. 11A and 11B show cross-sectional views of the heart similarly asFIGS. 9A and 9B. The imaging system displays the corresponding frontview 420A (shown in FIG. 12A) and left side view 450A (shown in FIG.12B). However, in the images of FIGS. 12A and 12B, the imaging systemuses different values for range gates 416 and 417 and for angular rangelines 412, 413, 445 and 446 than in FIGS. 10A and 10B since now distalpart 402 of catheter 400 is located now in the left ventricle 394.Furthermore, the imaging system displays a bottom view 500 (shown inFIG. 12C), instead of top view 470 (shown in FIG. 10C), after settingthe range gates 416A and 417A in FIGS. 12A and 12B.

FIG. 11A is a cross-sectional view of the heart along the long axiscross-section. The imaging system collects the echo data and generatesorthographic front view 420A, shown in FIG. 12A. The system uses a newazimuthal angular range delineated by lines 412A and 413A, which issmaller than the azimuthal angular range used for projection view 420.The smaller azimuthal angular range is selected because the surface ofinterest is located farther from array 42. In general, in the phasedarray mode, the imaging system images regions of interest located closeto array 42 using larger azimuthal and elevation angular ranges thanregions farther away.

Referring to FIG. 12A, front view 420A displays the septum 388, distalpart 402 of catheter 400, left ventricle 394, and portions of the mitralvalve 392 and aortic valve 395, all located within a range 414A. Frontview 420A can display distal part 402 of catheter 400 during, forexample, ablation or re-vascularization of the myocardial tissue. FIG.12A also displays front view icon 430A that includes array axis 432Alocated at an angle relative to an actual front view field 434Acorresponding to the azimuthal angular range defined by lines 412A and413A. Front view icon 430A includes an available front view field 436Acorresponding to a maximum azimuthal angular range. FIG. 11B is across-sectional view along the short axis of the heart. FIG. 11B showsdistal part 30 of probe 12 (located inside the esophagus 380) and distalpart 402 of ablation catheter 400, located inside the left ventricle394.

FIG. 12B displays left side view 450A and left side view icon 460A. Theimaging system generates left side view 450A, which shows a portion ofthe left ventricle 394, filled with oxygenated blood, and a portion ofthe right ventricle 386, filled with de-oxygenated blood. Distal part402 of catheter 400 is located near the distal surface 389A (bottomsurface) of the septum 388 within range gates 416A and 417A. Left sideview icon 460A shows an available side view field 462A and an actualside view field 464A. Actual side view field 464A displays theelevational angular range of the lines emitted from transducer array 42,which are delineated by lines 445A and 446A. Available side view field462A corresponds to a maximum elevation angular range.

FIGS. 11C and 11D are projection views of the human heart. FIG. 11Cshows a cut-away bottom view displaying distal part 402 and bottomsurface 389A of the septum 388, both of which are located within theranges defined in FIGS. 12A and 12B. FIG. 12C displays a C-scanprojection, bottom view 500, generated from the B-scan data within rangegates 416A and 417A. Bottom view 500 shows distal part 402 placed on thedistal surface (left ventricular surface) 389A of the septum 388. Rangegates 416A and 417A and angular range lines 412A, 413A, 446A, and 445Adefine the area of bottom view 500 in FIG. 12C. The area of bottom view500 is not identical to the shaded area due to the curvature of theproximal surface 389A. FIG. 12C also displays bottom view icon 520,which includes a rectangular array 522 and an array axis 524. The angleof axis 524, relative to the side of rectangular area 522 indicates theyaw angle of top view 500. The yaw angle is zero in this case.

The video display of the imaging system displays the above-describedorthographic projection views and the associated icons always at thesame location, shown in FIG. 7. The conventional location of each imageand icon makes it easier for a clinician to correlate the images to theactual anatomy of the imaged tissue. After providing another value ofyaw 160 (FIGS. 5 and 5A), the image generator recalculates allorthographic projection views and displays them at the standardlocations. Icon generators 289, 299 and 346 recalculate the data foricons 430A, 460A and 520, all of which are again displayed at thestandard locations. The displayed images have anatomically correctorientation.

FIGS. 13A and 13B show cross-sectional views of the heart similar toviews shown in FIGS. 11A and 11B, respectively. However, in FIGS. 13Aand 13B, the imaging system uses range gates 416B and 417B and forangular range lines 412B, 413B, 445B and 446B since distal part 402 ofcatheter 400 is located now in the left ventricle 394 on a tissuesurface 399. The imaging system displays a top view 470B (shown in FIG.14C), based on the setting of the range gates in FIGS. 14A and 14B.

FIGS. 13A and 13B show distal part 30 of probe 12 located inside theright ventricle 386 and a distal part 402 of ablation catheter 400 alsolocated inside the left ventricle 394. As described above, the imagingsystem uses transducer array 42 to collect the echo data and generateorthographic projection views shown in FIGS. 14A, 14B and 14C. The videodisplay displays the orthographic projection views and the associatedicon at the predetermined locations shown in FIGS. 7 and 7A.

Specifically, FIG. 14A shows a cross-sectional view 420B and a frontview icon 430B. Front view 420B shows distal catheter part 402positioned on tissue surface 399. Front view 420B also shows the mitralvalve 392 between the left ventricle 394 and the left atrium 390. Aclinician can set the location of gates 416B and 417B and an ROI marker415B. Front view icon 436B displays an array axis 432B and displays anavailable front view field 436B and an actual front view field 434B.Actual front view field 434B corresponds to the azimuthal angular rangedefined by lines 412B and 413B, and available front view field 436Bcorresponds to a maximum azimuthal angular range. The relationshipbetween actual view field 434B and available view field 436B displayspitch adjustment 181 (FIG. 5A(2)). Array axis 432B relative to actualview field 436B shows a selected value of yaw adjustment 183 (FIG.5A(2)).

Referring to FIGS. 13B and 14B, the imaging system can also generate aleft side view 450B by collecting echo data over a selected elevationangular range delineated by lines 445B and 446B and an ROI marker 448B.Left side view 450B displays a portion of the septum 388, and distalcatheter part 402, located on the left ventricular surface 399.Referring still to FIG. 132, left side view icon 460B displays anavailable side view field 462B and an actual side view field 464B, whichcorresponds to the elevation angle over which the image sectors wereacquired. The relationship between available view field 462B and actualview field 464B displays roll adjustment 182 (FIG. 5A(2)).

FIGS. 13C and 13D are projection views of the human heart. FIG. 13Dshows a cut-away top view displaying both distal part 30 of probe 12 anddistal part 402 of ablation catheter 400 located on the cardiac surface.FIG. 14C displays a C-scan projection, top view 470B, generated from theB-scan data within range gates 416B and 417B, and displays a top viewicon 490B. Top view 470B shows distal catheter part 402, located nearsurface 399, and a portion of the mitral valve 392. Range gates 416B and417B and angular range lines 412B, 413B, 445B, and 446B define the areaof top view 470B. FIG. 14C also displays top view icon 490B, whichincludes a rectangular array 492B and an array axis 494B. The angle ofaxis 494B relative to the side of rectangular area 492B indicates theyaw angle of top view 470B.

What is claimed is:
 1. A transesophageal imaging system including a TEEprobe comprising: an elongated semi-flexible body having a distal endand a proximal end; an articulating region coupled to the distal end ofthe elongated body; a distal tip coupled to the distal end of thearticulating region; a two dimensional array of transducer elementslocated at the distal tip and operable to electronically steer beamsover more than two planes of a volumetric region external to the lumenin which the distal tip is located; and a probe handle coupled to theproximal end of the elongated body, the probe handle including apositioning control coupled to the articulating region by means of theelongated body.
 2. The transesophageal imaging system of claim 1,wherein the distal tip further comprises an integrated circuit coupledto elements of the two dimensional array of transducer elements.
 3. Thetransesophageal imaging system of claim 2, wherein the distal tipfurther comprises an array backing located behind the two dimensionalarray of transducer elements.
 4. The transesophageal imaging system ofclaim 2, wherein the distal tip further comprises a heat sink which actsto conduct heat produced by the integrated circuit.
 5. Thetransesophageal imaging system of claim 1, wherein the elongatedsemi-flexible body comprises a gastroscope tube.
 6. The transesophagealimaging system of claim 1, wherein the elements of the two dimensionalarray of transducer elements are arranged into groups of sub-arrays. 7.The transesophageal imaging system of claim 6, further comprising aplurality of intra-group receive processors, each of which is coupled tothe elements of a sub-array.
 8. The transesophageal imaging system ofclaim 7, wherein each intra-group receive processor acts to delay andcombine signals received by the elements of an associated sub-array. 9.The transesophageal imaging system of claim 1, further comprising aparallel receive beamformer, responsive to signals received by elementsof the two dimensional array of transducer elements, which acts tosynthesize several receive beams simultaneously.
 10. The transesophagealimaging system of claim 1, further comprising an imaging systemresponsive to signals received by elements of the two dimensional arrayof transducer elements, which acts to produce one or more images inimage planes extending from the plane of the two dimensional array. 11.The transesophageal imaging system of claim 10, wherein the imagingsystem acts to produce a plurality of spatially different images; andfurther comprising an icon generator which acts to produce a displayicon indicating the relative orientation of the spatially differentimages.
 12. The transesophageal imaging system of claim 10, furthercomprising a display, coupled to the imaging system, which acts todisplay a plurality of spatially different images and a display iconsimultaneously.
 13. The transesophageal imaging system of claim 1,further comprising an imaging system, coupled to the TEE probe,including a boundary detector responsive to signals received by elementsof the two dimensional array of transducer elements, which acts todetect the outline of tissue scanned by the TEE probe.
 14. Thetransesophageal imaging system of claim 1, further comprising an imagegenerator, coupled to the TEE probe and responsive to signals receivedby elements of the two dimensional array of transducer elements, whichacts to generate a C-scan view.
 15. A method of transesophagealultrasonic imaging comprising: introducing into the esophagus a TEEprobe having a two-dimensional ultrasound transducer array which isoperable to electronically steer beams over more than two planes of avolumetric region external to the lumen in which the distal tip islocated; positioning the two-dimensional ultrasound transducer array ata selected orientation relative to the heart; transmitting ultrasoundbeams from the two-dimensional ultrasound transducer array over aplurality of transmit scan lines intersecting the heart; acquiring withthe two-dimensional ultrasound transducer array echo signals reflectedfrom the heart; processing the echo signals to generate an image of theheart; and displaying the generated image.
 16. The method of claim 15,further comprising, following the step of positioning, selecting animage plane of the heart which is to be displayed.
 17. The method ofclaim 16, wherein the TEE probe includes an articulating section, andwherein positioning comprises locking the articulating section tomaintain the two-dimensional ultrasound transducer array at a selectedorientation relative to the heart.
 18. The method of claim 16, furthercomprising, following the step of selecting, selecting a different imageplane of the heart for display.
 19. The method of claim 16, whereindisplaying comprises displaying the generated image together with anicon indicating the location of the image region relative to areference.
 20. The method of claim 15, further comprising, following thestep of positioning, selecting a tissue volume of the heart which is tobe displayed.
 21. The method of claims 20, wherein transmittingcomprises transmitting ultrasound beams over an azimuthal range and anelevation range of locations corresponding to the selected tissuevolume.